Biomedical subjects

V Rosen

Publications and source records attributed to V Rosen.

At least 19 recordsLinked to original sources

PubMed2002

The localized expression of extracellular matrix components in healing tendon insertion sites: an in situ hybridization study.

The localized expression of a number of extracellular matrix genes was evaluated over time in a novel rat rotator cuff injury model. The supraspinatus tendons of rats were severed at the bony insertion and repaired surgically. The healing response was evaluated at 1, 2, 4, and 8 weeks post-injury using histologic and in situ hybridization techniques. Expression patterns of collagens (I, II, III, IX, X, XII), proteoglycans (decorin, aggrecan, versican, biglycan, fibromodulin), and other extracellular matrix proteins (elastin, osteocalcin, alkaline phosphatase) were evaluated at the healing tendon to bone insertion site. Histologic results indicate a poor healing response to the injury, with only partial recreation of the insertion site by 8 weeks. In situ hybridization results indicate a specific pattern of genes expressed in each zone of the insertion site (i.e., tendon, fibrocartilage, mineralized cartilage, bone). Overall, expression of collagen types I and XII, aggrecan, and biglycan was increased, while expression of collagen type X and decorin was decreased. Expression of collagen type I, collagen type XII, and biglycan decreased over time, but remained above normal at 8 weeks. Results indicate that the rat supraspinatus tendon is ineffective in recreating the original insertion site, even at 8 weeks post-injury, in the absence of biological or biomechanical enhancements.

Animals↗

PubMed2001

Gdf11 is a negative regulator of chondrogenesis and myogenesis in the developing chick limb.

GDF11, a new member of the TGF-beta gene superfamily, regulates anterior/posterior patterning in the axial skeleton during mouse embryogenesis. Gdf11 null mice display skeletal abnormalities that appear to represent anterior homeotic transformations of vertebrae consistent with high levels of Gdf11 expression in the primitive streak, presomitic mesoderm, and tail bud. However, despite strong Gdf11 expression in the limb throughout development, this structure does not appear to be affected in the knockout mice. In order to understand this dichotomy of Gdf11 expression versus Gdf11 function, we identified the chicken Gdf11 gene and studied its role during limb formation. In the early limb bud, Gdf11 transcripts are detected in the subectodermal mesoderm at the distal tip, in a region overlapping the progress zone. At these stages, Gdf11 is excluded from the central core mesenchyme where precartilaginous condensations will form. Later in development, Gdf11 continues to be expressed in the distal most mesenchyme and can also be detected more proximally, in between the forming skeletal elements. When beads incubated in GDF11 protein were implanted into the early wing bud, GDF11 caused severe truncations of the limb that affected both the cartilage elements and the muscle. Limb shortening appeared to be the result of an inhibition of chondrogenesis and myogenesis and using an in vitro micromass assay, we confirmed the negative effects of GDF11 on both myogenic and chondrogenic cell differentiation. Analysis of molecular markers of skeletal patterning revealed that GDF11 induced ectopic expression of Hoxd-11 and Hoxd-13, but not of Hoxa-11, Hoxa-13, or the Msx genes. These data suggest that GDF11 may be involved in controlling the late distal expression of the Hoxd genes during limb development and that misregulation of these Hox genes by excess GDF11 may cause some of the observed alterations in skeletal element shape. In addition, GDF11 induced the expression of its own antagonist follistatin, indicating that the activity of GFD11 may be limited by a negative feedback mechanism. The data from our studies in the chick suggest that Gdf11 plays a role in the formation and development of the avian limb skeleton.

Animals↗

PubMed2001

Bone morphogenetic protein-3 is a negative regulator of bone density.

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGF-beta) superfamily. Many BMPs are produced in bone and show osteogenic activity, suggesting that they may be determinants of bone mass. BMP3 was originally purified from bone as osteogenin, which induces osteogenic differentiation. Recombinant BMP3 (rhBMP3) has no biological activity, however, leaving its role in skeletal growth unclear. Here we show that BMP3 is an antagonist of osteogenic BMPs: BMP3 dorsalizes Xenopus laevis embryos, inhibits BMP2-mediated induction of Msx2 and blocks BMP2-mediated differentiation of osteoprogenitor cells into osteoblasts. These effects appear to be mediated through activin receptors. Finally, Bmp3(-/-) mice have twice as much trabecular bone as wild-type littermates, indicating that BMP3, the most abundant BMP in adult bone, is a negative determinant of bone density.

Activin Receptors↗

PubMed2001

Differential regulation of the two principal Runx2/Cbfa1 n-terminal isoforms in response to bone morphogenetic protein-2 during development of the osteoblast phenotype.

Cbfa1/Runx2 is a transcription factor essential for bone formation and osteoblast differentiation. Two major N-terminal isoforms of Cbfa1, designated type I/p56 (PEBP2aA1, starting with the sequence MRIPV) and type II/p57 (til-1, starting with the sequence MASNS), each regulated by distinct promoters, are known. Here, we show that the type I transcript is constitutively expressed in nonosseous mesenchymal tissues and in osteoblast progenitor cells. Cbfa1 type I isoform expression does not change with the differentiation status of the cells. In contrast, the type II transcript is increased during differentiation of primary osteoblasts and is induced in osteoprogenitors and in premyoblast C2C12 cells in response to bone morphogenetic protein-2. The functional equivalence of the two isoforms in activation and repression of bone-specific genes indicates overlapping functional roles. The presence of the ubiquitous type I isoform in nonosseous cells and before bone morphogenetic protein-2 induced expression of the type II isoform suggests a regulatory role for Cbfa1 type I in early stages of mesenchymal cell development, whereas type II is necessary for osteogenesis and maintenance of the osteoblast phenotype. Our data indicate that Cbfa1 function is regulated by transcription, cellular protein levels, and DNA binding activity during osteoblast differentiation. Taken together, our studies suggest that developmental timing and cell type- specific expression of type I and type II Cbfa isoforms, and not necessarily molecular properties or sequences that reside in the N-terminus of Cbfa1, are the principal determinants of the osteogenic activity of Cbfa1.

Animals↗

PubMed2001

Analysis of the tendon cell fate using Scleraxis, a specific marker for tendons and ligaments.

Little is known about the genesis and patterning of tendons and other connective tissues, mostly owing to the absence of early markers. We have found that Scleraxis, a bHLH transcription factor, is a highly specific marker for all the connective tissues that mediate attachment of muscle to bone in chick and mouse, including the limb tendons, and show that early scleraxis expression marks the progenitor cell populations for these tissues. In the early limb bud, the tendon progenitor population is found in the superficial proximomedial mesenchyme. Using the scleraxis gene as a marker we show that these progenitors are induced by ectodermal signals and restricted by bone morphogenetic protein (BMP) signaling within the mesenchyme. Application of Noggin protein antagonizes this endogenous BMP activity and induces ectopic scleraxis expression. However, the presence of excess tendon progenitors does not lead to the production of additional or longer tendons, indicating that additional signals are required for the final formation of a tendon. Finally, we show that the endogenous expression of noggin within the condensing digit cartilage contributes to the induction of distal tendons.

Animals↗

PubMed2000

Regulation of skeletal progenitor differentiation by the BMP and retinoid signaling pathways.

The generation of the paraxial skeleton requires that commitment and differentiation of skeletal progenitors is precisely coordinated during limb outgrowth. Several signaling molecules have been identified that are important in specifying the pattern of these skeletal primordia. Very little is known, however, about the mechanisms regulating the differentiation of limb mesenchyme into chondrocytes. Overexpression of RARalpha in transgenic animals interferes with chondrogenesis and leads to appendicular skeletal defects (Cash, D.E., C.B. Bock, K. Schughart, E. Linney, and T.M. Underhill. 1997. J. Cell Biol. 136:445-457). Further analysis of these animals shows that expression of the transgene in chondroprogenitors maintains a prechondrogenic phenotype and prevents chondroblast differentiation even in the presence of BMPs, which are known stimulators of cartilage formation. Moreover, an RAR antagonist accelerates chondroblast differentiation as demonstrated by the emergence of collagen type II-expressing cells much earlier than in control or BMP-treated cultures. Addition of Noggin to limb mesenchyme cultures inhibits cartilage formation and the appearance of precartilaginous condensations. In contrast, abrogation of retinoid signaling is sufficient to induce the expression of the chondroblastic phenotype in the presence of Noggin. These findings show that BMP and RAR-signaling pathways appear to operate independently to coordinate skeletal development, and that retinoid signaling can function in a BMP-independent manner to induce cartilage formation. Thus, retinoid signaling appears to play a novel and unexpected role in skeletogenesis by regulating the emergence of chondroblasts from skeletal progenitors.

Animals↗

PubMed2000

Cloning and expression of the Wnt antagonists Sfrp-2 and Frzb during chick development.

The Wnt genes are known to play fundamental roles during patterning and development of a number of embryonic structures. Receptors for Wnts are members of the Frizzled family of proteins containing a cysteine-rich domain (CRD) that binds the Wnt protein. Recently several secreted frizzled-related proteins (Sfrps) that also contain a CRD have been identified and some of these can both bind and antagonise Wnt proteins. In this paper we report the expression patterns of the chick homologues of Frzb, a known Wnt antagonist, and Sfrp-2. Both genes are expressed in areas where Wnts are known to play a role in development, including the neural tube, myotome, cartilage, and sites of epithelial-mesenchymal interactions. Initially, Sfrp-2 and Frzb are expressed in overlapping areas in the neural plate and neural tube, whereas later, they have distinct patterns. In particular Sfrp-2 is associated with myogenesis while Frzb is associated with chondrogenesis, suggesting that they play different roles during development. Finally, we have used the early Xenopus embryo as an in vivo assay to show that Sfrp-2, like Frzb, is a Wnt antagonist. These results suggest that Sfrp-2 and Frzb may function in the developing embryo by modulating Wnt signalling.

Amino Acid Sequence↗

PubMed2000

The type I BMP receptor BMPRIB is required for chondrogenesis in the mouse limb.

Mice carrying a targeted disruption of BmprIB were generated by homologous recombination in embryonic stem cells. BmprIB(-/-) mice are viable and, in spite of the widespread expression of BMPRIB throughout the developing skeleton, exhibit defects that are largely restricted to the appendicular skeleton. Using molecular markers, we show that the initial formation of the digital rays occurs normally in null mutants, but proliferation of prechondrogenic cells and chondrocyte differentiation in the phalangeal region are markedly reduced. Our results suggest that BMPRIB-mediated signaling is required for cell proliferation after commitment to the chondrogenic lineage. Analyses of BmprIB and Gdf5 single mutants, as well as BmprIB; Gdf5 double mutants suggests that GDF5 is a ligand for BMPRIB in vivo. BmprIB; Bmp7 double mutants were constructed in order to examine whether BMPRIB has overlapping functions with other type I BMP receptors. BmprIB; Bmp7 double mutants exhibit severe appendicular skeletal defects, suggesting that BMPRIB and BMP7 act in distinct, but overlapping pathways. These results also demonstrate that in the absence of BMPRIB, BMP7 plays an essential role in appendicular skeletal development. Therefore, rather than having a unique role, BMPRIB has broadly overlapping functions with other BMP receptors during skeletal development.

Animals↗

PubMed1999

Different effects of bone morphogenetic proteins 2, 4, 12, and 13 on the expression of cartilage and bone markers in the MC615 chondrocyte cell line.

In order to study the lineage leading to chondrocyte and osteoblast phenotype in vertebrate development, we examined the effect of recombinant human bone morphogenetic protein (BMP)-2, BMP-4, BMP-12 [or growth and differentiation factor (GDF)-7], and BMP-13 (or GDF-6) on the phenotypic expression of the mouse chondrocyte cell line MC615, grown for 1 or 2 weeks in monolayer. Protein synthesis rates were monitored after incubation with [(14)C]proline. BMP-2 and BMP-4 increased protein synthesis, in agreement with our observation by phase-contrast microscopy of a highly refractile matrix around MC615 cells treated with BMP-2 and -4. Markers of the chondrocytic and osteoblastic differentiation were analyzed at mRNA level. Expression of the type II collagen gene, a marker of the cartilage phenotype, was up-regulated in the presence of low concentration of BMP-2 or -4 (50 ng/ml) and down-regulated at higher concentrations (100-400 ng/ml). In parallel, this expression was stable in the presence of BMP-12 or -13 in the dose range tested (50-400 ng/ml). Expression of the matrix Gla protein (MGP) gene, another marker of cartilage, was also reduced in the presence of 100 ng/ml BMP-2 or -4, while it remained stable in the presence of BMP-12 or -13 at the same concentration. In contrast, expression of the bone Gla protein (BGP) gene, or osteocalcin, a marker of the bone phenotype, was induced when the cells were treated with BMP-2 or -4 but was not detected when the cells were treated with BMP-12 or -13. At the same time, BMP-2 or -4 markedly up-regulated expression of type X collagen mRNA, indicating that MC615 cells possess the ability to express traits associated with endochondral ossification, when exposed to specific BMPs. Furthermore, detailed analysis of type II collagen expression showed that the alternatively spliced transcript collagen IIB, specific for cartilage, is expressed concomitantly with BGP. Therefore, MC615 chondrocytes can simultaneously express chondrocytic and osteoblastic markers, in response to BMP-2 or -4, but show minimal response to BMP-12 (or GDF-7) or to BMP-13 (or GDF-6). These results raise the possibility that chondrocytes in vivo can express osteoblastic properties, provided they are induced by BMP-2 or -4.

Animals↗

PubMed1999

A novel BMP expressed in developing mouse limb, spinal cord, and tail bud is a potent mesoderm inducer in Xenopus embryos.

The bone morphogenetic proteins (BMPs) play critical roles in patterning the early embryo and in the development of many organs and tissues. We have identified a new member of this multifunctional gene family, BMP-11, which is most closely related to GDF-8/myostatin. During mouse embryogenesis, BMP-11 is first detected at 9.5 dpc in the tail bud with expression becoming stronger as development proceeds. At 10.0 dpc, BMP-11 is expressed in the distal and posterior region of the limb bud and later localizes to the mesenchyme between the skeletal elements. BMP-11 is also expressed in the developing nervous system, in the dorsal root ganglia, and dorsal lateral region of the spinal cord. To assess the biological activity of BMP-11, we tested the protein in the Xenopus ectodermal explant (animal cap) assay. BMP-11 induced axial mesodermal tissue (muscle and notochord) in a dose-dependent fashion. At higher concentrations, BMP-11 also induced neural tissue. Interestingly, the activin antagonist, follistatin, but not noggin, an antagonist of BMPs 2 and 4, inhibited BMP-11 activity on animal caps. Our data suggest that in Xenopus embryos, BMP-11 acts more like activin, inducing dorsal mesoderm and neural tissue, and less like other family members such as BMPs 2, 4, and 7, which are ventralizing and anti-neuralizing signals. Taken together, these data suggest that during vertebrate embryogenesis, BMP-11 plays a unique role in patterning both mesodermal and neural tissues.

Amino Acid Sequence↗

PubMed1999

Transient upregulation of CBFA1 in response to bone morphogenetic protein-2 and transforming growth factor beta1 in C2C12 myogenic cells coincides with suppression of the myogenic phenotype but is not sufficient for osteoblast differentiation.

The bone morphogenetic protein (BMP)-2 is a potent osteoinductive signal, inducing bone formation in vivo and osteoblast differentiation from non-osseous cells in vitro. The runt domain-related protein Cbfa1/PEBP2alphaA/AML-3 is a critical component of bone formation in vivo and transcriptional regulator of osteoblast differentiation. To investigate the relationship between the extracellular BMP-2 signal, Cbfa1, and osteogenesis, we examined expression of Cbfa1 and osteoblastic genes during the BMP-2 induced osteogenic transdifferentiation of the myoblastic cell line C2C12. BMP-2 treatment completely blocked myotube formation and transiently induced expression of Cbfa1 and the bone-related homeodomain protein Msx-2 concomitant with loss of the myoblast phenotype. While induction of collagen type I and alkaline phosphatase (AP) expression coincided with Cbfa1 expression, Cbfa1 mRNA was strikingly downregulated at the onset of expression of osteopontin (OPN) and osteocalcin (OCN) genes, reflecting the mature osteoblast phenotype. TGF-beta1 treatment effectively suppressed myogenesis and induced Cbfa1 expression but was insufficient to support osteoblast differentiation reflected by the absence of ALP, OPN, and OCN. We addressed whether induction of Cbfa1 in response to BMP-2 results in the transcriptional activation of the OC promoter which contains three enhancer Cbfa1 elements. Transfection studies show BMP-2 suppresses OC promoter activity in C2C12, but not in osteoblastic ROS 17/2.8 cells. Maximal suppression of OC promoter activity in response to BMP-2 requires sequences in the proximal promoter (up to nt -365) and may occur independent of the three Cbfa sites. Taken together, our results demonstrate a dissociation of Cbfa1 expression from development of the osteoblast phenotype. Our findings suggest that Cbfal may function transiently to divert a committed myoblast to a potentially osteogenic cell. However, other factors induced by BMP-2 appear to be necessary for complete expression of the osteoblast phenotype.

Animals↗

PubMed1999

Effects of GDF7/BMP12 on proliferation and alkaline phosphatase expression in rat osteoblastic osteosarcoma ROS 17/2.8 cells.

Growth and differentiation factor 7(GDF7), also later called as bone morphogenetic protein (BMP)12, is a new member of the BMP superfamily, which induces formation of tendon-like tissue formation in the ectopic implantation experiments. We examined the effect of BMP12 on proliferation and expression of phenotype-related genes in rat osteoblastic osteosarcoma ROS17/2.8 cells. BMP12 treatment enhanced proliferation of ROS17/2.8 cells within 3 days and this effect was observed at least up to day 6 of the treatment. The cell number was increased by about 50% on day 3 and about two-fold by day 6. These effects were observed at the dose range between 40 and 1,000 ng/ml. Treatment with BMP12 also enhanced alkaline phosphatase activity by about 50% in ROS17/2.8 cells within 24 h of the treatment. The effect peaked at 48 h and was still observed at 72 h. The enhancing effect of BMP12 on alkaline phosphatase was observed similarly at the doses ranging from 40 to 1,000 ng/ml. These data indicate that BMP12 has positive effects on proliferation and phenotypic expression of ROS 17/2.8 cells.

Alkaline Phosphatase↗

PubMed1999

Heart specific expression of mouse BMP-10 a novel member of the TGF-beta superfamily.

Here we report the cloning and expression of murine BMP-10, a novel member of the TGF-beta superfamily. In the mouse embryo, BMP-10 expression begins at 9.0 d.p.c. and is restricted to the developing heart. Initially, BMP-10 expression localizes to the trabeculated part of the common ventricular chamber and to the bulbus cordis region. After 12.5 d.p.c., additional BMP-10 expression is seen in the atrial wall. The data presented here suggest that BMP-10 plays an important role in trabeculation of the embryonic heart.

Amino Acid Sequence↗

PubMed1998

Differential roles for bone morphogenetic protein (BMP) receptor type IB and IA in differentiation and specification of mesenchymal precursor cells to osteoblast and adipocyte lineages.

Cumulative evidence indicates that osteoblasts and adipocytes share a common mesenchymal precursor and that bone morphogenetic proteins (BMPs) can induce both osteoblast and adipocyte differentiation of this precursor. In the present study, we investigated the roles of BMP receptors in differentiation along these separate lineages using a well-characterized clonal cell line, 2T3, derived from the mouse calvariae. BMP-2 induced 2T3 cells to differentiate into mature osteoblasts or adipocytes depending upon culture conditions. To test the specific roles of the type IA and IB BMP receptor components, truncated and constitutively active type IA and IB BMP receptor cDNAs were stably expressed in these cells. Overexpression of truncated type IB BMP receptor (trBMPR-IB) in 2T3 cells completely blocked BMP-2-induced osteoblast differentiation and mineralized bone matrix formation. Expression of trBMPR-IB also blocked mRNA expression of the osteoblast specific transcription factor, Osf2/ Cbfa1, and the osteoblast differentiation-related genes, alkaline phosphatase (ALP) and osteocalcin (OC). BMP-2-induced ALP activity could be rescued by transfection of wild-type (wt) BMPR-IB into 2T3 clones containing trBMPR-IB. Expression of a constitutively active BMPR-IB (caBMPR-IB) induced formation of mineralized bone matrix by 2T3 cells without addition of BMP-2. In contrast, overexpression of trBMPR-IA blocked adipocyte differentiation and expression of caBMPR-IA induced adipocyte formation in 2T3 cells. Expression of the adipocyte differentiation-related genes, adipsin and PPARgamma, correlated with the distinct phenotypic changes found after overexpression of the appropriate mutant receptors. These results demonstrate that type IB and IA BMP receptors transmit different signals to bone-derived mesenchymal progenitors and play critical roles in both the specification and differentiation of osteoblasts and adipocytes.

Adipocytes↗

PubMed1998

Bone morphogenetic protein and bone morphogenetic protein gene family in bone formation and repair.

The bone morphogenetic proteins are secreted signalling molecules that belong to the transforming growth factor beta family of growth and differentiation factors. Individual bone morphogenetic proteins are prominent at many sites during embryogenesis and are likely to be key regulators of early development and organogenesis. In vertebrates, one of the functions of bone morphogenetic like proteins is to induce formation of bone, cartilage, and connective tissues associated with the skeleton. This osteoinductive ability has led to the use of bone morphogenetic proteins as therapeutic agents for creation of new bone useful in treatment of skeletal injuries and diseases, and in oral and maxillofacial applications.

Animals↗

PubMed1998

Characterization of bone morphogenetic protein 4 receptor in fibrodysplasia ossificans progressiva.

Bone morphogenetic protein 4, a potent osteogenic morphogen, has been implicated in fibrodysplasia ossificans progressiva because it is uniquely overexpressed in lymphoblastoid cells and preosseous fibroproliferative lesional cells of patients with fibrodysplasia ossificans progressiva. Bone morphogenetic protein 4 signals through a heteromeric complex of serine/ threonine kinase receptors (type I and type II) on the surface of responding cells. Semi-quantitative competitive reverse transcription polymerase chain reaction was used to quantitate steady state levels of messenger ribonucleic acid expression for bone morphogenetic protein 4 and the bone morphogenetic protein receptors. These data confirmed the previous finding of elevated steady state levels of bone morphogenetic protein 4 messenger ribonucleic acid in lymphoblastoid cell lines of affected individuals in a family that exhibited autosomal dominant inheritance of fibrodysplasia ossificans progressiva. There were no differences in the steady state levels of messenger ribonucleic acid for either the Type I or Type II bone morphogenetic protein 4 receptors between affected and unaffected individuals in that same family. The presence of bone morphogenetic protein 4 receptor messenger ribonucleic acid in fibrodysplasia ossificans progressiva lesional tissue and unaffected muscle tissue and demonstrates the deregulation of bone morphogenetic protein 4 messenger ribonucleic acid in fibrodysplasia ossificans progressiva. These data support the hypothesis that the molecular basis of bone morphogenetic protein 4 signaling is abnormal in fibrodysplasia ossificans progressiva.

Bone Morphogenetic Protein 4↗

PubMed1997

Opposing effects by glucocorticoid and bone morphogenetic protein-2 in fetal rat bone cell cultures.

Glucocorticoid in excess produces bone loss in vivo. Consistent with this, it reduces the stimulatory effect of transforming growth factor beta (TGF-beta) on collagen synthesis in osteoblast-enriched cultures in vitro, where it also suppresses TGF-beta binding to its type I receptors. Analogous studies with bone morphogenetic protein-2 (BMP-2) show directly opposite results. These findings prompted us to assess the effect of glucocorticoid on BMP-2 activity in cultured bone cells, and whether either agent had a dominant influence on TGF-beta binding or function. BMP-2 activity was retained in part in osteoblast-enriched cultures pre-treated or co-treated with cortisol, and was fully evident when glucocorticoid exposure followed BMP-2 treatment. In addition, BMP-2 suppressed the effects of cortisol on TGF-beta activity, on TGF-beta binding, and on gene promoter activity directed by a glucocorticoid sensitive transfection construct. While BMP-2 also alters the function of less-differentiated bone cells, it only minimally prevented cortisol activity in these cultures. Our studies indicate that BMP-2 can oppose certain effects by cortisol on differentiated osteoblasts, and may reveal useful ways to diminish glucocorticoid-dependent bone wasting.

Activin Receptors, Type I↗

PubMed1997

A kinase domain-truncated type I receptor blocks bone morphogenetic protein-2-induced signal transduction in C2C12 myoblasts.

Members of the transforming growth factor (TGF)-beta superfamily bind the transmembrane serine/threonine kinase complex consisting of type I and type II receptors. Their intracellular signals are propagated via respective type I receptors. Bone morphogenetic protein (BMP)-2, a member of the TGF-beta superfamily, induces ectopic bone formation when implanted into muscular tissues. Two type I receptors (BMPR-IA and BMPR-IB) have been identified for BMP-2. We have reported that BMP-2 inhibits the terminal differentiation of C2C12 myoblasts and converts their differentiation pathway into that of osteoblast lineage cells (Katagiri, T., Yamaguchi, A., Komaki, M., Abe, E., Takahashi, N., Ikeda, T., Rosen, V., Wozney, J. M., Fujisawa-Sehara, A. and Suda, T. (1994) J. Cell Biol. 127, 1755-1766). In the present study, we examined the involvement of functional BMP-2 type I receptors in signal transduction in C2C12 cells, which expressed mRNA for BMPR-IA, but not for BMPR-IB in Northern blotting. TGF-beta type I receptor (TbetaR-I) mRNA was also expressed in C2C12 cells. Subclonal cell lines of C2C12 that stably expressed a kinase domain-truncated BMPR-IA (DeltaBMPR-IA) differentiated into myosin heavy chain-expressing myotubes but not into alkaline phosphatase (ALP)-positive cells, even in the presence of BMP-2. In contrast, the differentiation of the DeltaBMPR-IA-transfected C2C12 cells into myotubes was suppressed by TGF-beta1, as in the parental C2C12 cells. BMP-2 did not efficiently suppress the mRNA expression of muscle-specific genes such as muscle creatine kinase, MyoD, and myogenin, nor did it induce the expression of ALP mRNA in the DeltaBMPR-IA-transfected C2C12 cells. In contrast, TGF-beta1 inhibited mRNA expression of the muscle-specific genes in those cells. When wild-type BMPR-IA was transiently transfected into the DeltaBMPR-IA-transfected C2C12 cells, a number of ALP-positive cells appeared in the presence of BMP-2. Transfection of wild-type BMPR-IB or TbetaR-I failed to increase the number of ALP-positive cells. These results suggest that the BMP-2-induced signals, which inhibit myogenic differentiation and induce osteoblast differentiation, are transduced via BMPR-IA in C2C12 myoblasts.

Affinity Labels↗